Nearly every power generating plant—be it a nuclear power plant, a cogeneration plant, a wind power station—generates the current by a generator which converts mechanical energy into electrical power.
Usually, the generator is connected to a power line conducting electrical current. The power line from which consumer loads connected to it obtain their power, should have a defined grid parameters, in particular, a defined voltage and a defined frequency. For example, the desired values for the average German household on the low voltage level are 230 Volts and 50 Hertz (Hz).
The stability of the grid parameters is dependent on a variety of influencing variables including the balance between generated power and the consumed power at every instant. Any imbalance between generated (real) power and consumed (real) power leads to changes in the grid frequency. When more power is generated than consumed, the frequency rises, if more power is consumed than generated, it decreases. In order to avoid overload within the combined grid systems and to control the load flow, it is vital to maintain the grid frequency fluctuation as small as possible.
As the installed power of wind turbines increases, wind power generation has an increasing influence on the grid stability. Therefore, it becomes more and more important for wind farms to contribute to the grid stabilization by controlling the real power output of a wind farm dependent on the grid frequency.